1. Technical Field
The present invention relates to an optical module widely used for an image processing apparatus such as a copier and a scanner, an image reader including the optical module concerned and an assembling method of an optical module.
2. Background Art
An image reader such as a copier and a scanner are always requested to be miniaturized and to cut cost. An image reader includes an optical module which reads image information from a manuscript arranged on a platen glass. A general optical module reads image information from an image by reciprocating along a guide rail arranged under a manuscript. Further, a mechanism to let an optical module reciprocate is disclosed, for example, in patent document 1 (Japanese Patent Application Laid-Open No. 2003-295339).
An optical module is described. FIG. 20 shows an example of a lateral sectional view of a general optical module. In FIG. 20, there is a light source 12 which irradiates a reading surface of a manuscript 11 above an optical module 10. In FIG. 20, the light source 12 is a stick type illuminant whose longitudinal direction is vertical to a sheet. Hereinafter, a direction vertical to a sheet is described as a main scanning direction.
A linear ray of light emitted from the light source 12 irradiates the manuscript 11 along a main scanning direction. Reflected light 13 from the manuscript 11 enters a first reflective mirror 15 arranged in a housing 14. Then, a ray of light reflected by a reflective mirror 15 enters an optical lens unit 19 via a second to a fourth reflective mirror 16-18. A ray of light 20 emitted from the optical lens unit 19 forms an image on a CCD (Charge Coupled Device) 21, and image information on the manuscript 11 is read line by line. Further, in order to set an optical path with a high degree of accuracy, a reflective mirror group 15-18, the optical lens unit 19 and the CCD 21 are generally arranged in an housing together.
Here, because the length of a single line of the manuscript 11 is larger than the length of a detection length of the CCD 21, an optical path length from the manuscript 11 to the optical lens unit 19 needs to be set longer compared with an optical path length from the optical lens unit 19 to a reading surface of a CCD 21. Also, in the housing 14, an optical path needs to be set avoiding the optical lens unit 19. In order to avoid the optical lens unit 19 and set a long optical path, a plurality of reflective mirrors 15-18 need to be arranged separately in left, right, above or below, and the housing 14 becomes large.
Accordingly, patent document 2 (Japanese Patent Application Laid-Open No. 2005-198230) discloses a technology which lowers a height of a housing by arranging separately a plurality of reflective mirrors on one side of an optical lens unit and a CCD on the other side. FIG. 21 shows a lateral sectional view of an optical module disclosed in patent document 2. In FIG. 21, in a housing 14B, a plurality of reflective mirrors 15B-18B are arranged on one side of an optical lens unit 19B, and a CCD 21B on the other side. When a plurality of reflective mirrors 15B-18B are arranged together on one side of the optical lens unit 19B, an optical path need not be set avoiding the optical lens unit 19B. In this case, a plurality of reflective mirrors 15B-18B can be arranged within a fixed height. Accordingly, a height of the housing 14B can be made low. Further, also in FIG. 21, in order to set an optical path with a high degree of accuracy, a plurality of reflective mirrors 15B-18B, the optical lens unit 19B and the CCD 21B are arranged within the housing 14B together.